Ruby and Rails Interview Questions & Answers
1. Ruby - Debugging and Troubleshooting
Q: How do you handle unexpected nil errors in Ruby?
A: Use safe navigation (&.), presence checks (nil?, blank?), and wrap logic with guard clauses.
Q: What’s your approach for debugging intermittent issues in a long-running Ruby service?
A: Add granular logs, capture runtime state using binding.irb or puts, monitor memory/CPU usage, and replicate conditions in test environments.
Q: How do you handle exceptions in a resilient Ruby script?
A: Use begin-rescue, log detailed error info, retry for transient errors, and alert for persistent ones.
2. Ruby - Code Quality and Maintenance
Q: How do you write maintainable Ruby code? A: Follow SOLID principles, avoid deep nesting, prefer small methods and service objects.
Q: What’s your strategy for managing large modules? A: Break into smaller modules or mixins, use namespacing, and limit coupling.
Q: How do you refactor duplicated Ruby logic? A: Extract to helper methods, modules, or use DRY abstractions like lambdas or shared service objects.
3. Rails - Request Handling & Controller Design
Q: How do you prevent large controller actions in Rails?
A: Move logic to services, use before_action filters smartly, and keep controllers RESTful.
Q: How do you handle conditional rendering in controllers?
A: Use respond_to, head, or service-driven decorators for clean output rendering.
Q: What are strong parameters and why are they important? A: They whitelist permitted params to prevent mass-assignment vulnerabilities.
4. Rails - Model Optimization
Q: How do you handle large or complex model methods? A: Extract logic into scopes, class methods, or move to service/interactor classes.
Q: What’s your approach for validating dependent attributes? A: Use custom validations with conditionals and add test coverage for edge cases.
Q: How do you handle dirty tracking or change detection in models?
A: Use ActiveModel’s attribute_changed?, saved_change_to_attribute, and callbacks.
5. Rails - Frontend Integration & APIs
Q: How do you structure a Rails API response?
A: Use serializers like ActiveModel::Serializer or Jbuilder, ensure consistent formats.
Q: How do you handle authentication for APIs? A: Use JWT or OAuth with middleware, and enforce authorization at the controller level.
Q: How do you handle versioning in Rails APIs?
A: Namespace routes (e.g., api/v1) and separate controllers/serializers by version.
6. Rails - Security and Resilience
Q: How do you prevent SQL Injection in Rails? A: Use ActiveRecord methods, parameterized queries, and avoid string interpolation in queries.
Q: How do you prevent CSRF in Rails?
A: Enable the authenticity token mechanism and use protect_from_forgery in controllers.
Q: How do you secure sensitive credentials?
A: Use Rails credentials (config/credentials.yml.enc), and never commit secrets to version control.
7. Rails - Real-world Scenarios & Debugging
Q: How do you debug a delayed Sidekiq job not being executed? A: Check job queues, logs, retry/delay settings, Redis connection, and background processor status.
Q: How do you monitor a memory-intensive Rails process?
A: Use ps, top, or htop, check logs for GC stats, and use tools like New Relic or Scout.
Q: How do you recover a stuck deployment or migration? A: Roll back or fix the migration manually, investigate locks, and use transactional safety mechanisms.
Let me know if you’d like questions for Docker, AWS, or frontend tech like Angular next!